This application is based on patent application Hei.11-31815 filed in Japan, the content of which are hereby incorporated by references.
1. Field of the Invention
This invention relates to an apparatus and a method for measuring a spectral property of a fluorescent sample including a fluorescent material.
2. Description of the Related Art
Generally, a visual property of a fluorescent sample including a fluorescent material is shown by a total spectral radiant factor. The total spectral radiant factor is a ratio by each wavelength of an emitted light from a sample which is illuminated under a predetermined condition against an emitted light from a perfect reflection diffuser illuminated under the same condition. The total spectral radiant factor Bt(xcex) is shown by the following equation (1).
Bt(xcex)=Br(xcex)+Bf(xcex)xe2x80x83xe2x80x83(1)
Hereupon, Br(xcex) is a reflecting spectral radiant factor owing to a reflected light component from the fluorescent sample and Bf(xcex) is a fluorescent spectral radiant factor owing to a fluorescent light component from the fluorescent sample.
A fluorescent sample having a spectral excitation effect F(xcexc, xcex) is generally excited by a light having a wavelength xcexc in ultraviolet (hereinafter abbreviated as UV) region included in the illumination. Thus, the fluorescent spectral radiant factor Bf(xcex) is shown by the following equation (2).
Bf(xcex)=∫UVI(xcexc)xc2x7F(xcexc,xcex)dxcexc/L(xcex)xe2x80x83xe2x80x83(2)
Hereupon, I(xcex) is a spectral intensity distribution of an illumination light and L(xcex) is a spectral intensity distribution of a standardized illumination light. As can be shown by the above-mentioned equation, the fluorescent spectral radiant factor Bf(xcex) depends on the spectral intensity distribution of the illumination light.
When a standard non-fluorescent white sample, in which a reflection spectral radiant factor Brw(xcex) thereof is known, is measured by a calorimeter, spectral intensities of the emitted light from the standard sample and the reference light are respectively designated by Sw(xcex) and Rw(xcex). When a fluorescent sample is measured by the calorimeter, spectral intensities of the emitted light from the fluorescent sample and the reference light are respectively designated by S(xcex) and R(xcex). The total spectral radiant factor Bt(xcex) of the fluorescent sample is shown by the following equation (3).
Bt(xcex)=Brw(xcex)xc2x7{(S(xcex)/R(xcex)}/{Sw(xcex)/Rw(xcex)}xe2x80x83xe2x80x83(3)
As mentioned above, the total spectral radiant factor of the fluorescent sample depends on the spectral intensity of the illumination light, so that it is necessary to coincide the spectral intensity distribution of the illumination light with the spectral intensity distribution of an assumed illumination light used for the measurement.
As an illumination light, a standard D65 illuminant (day light) and a standard A illuminant (incandescent lamp) are well known. Furthermore, D50, D55 and D75 illuminants (day light) and F1, F3 and F11 illuminants (fluorescent lamp) are known. Spectral intensity distribution of these illuminants are defined by CIE (Commission Internationale de I""Eclairage).
In the estimation of the fluorescent sample, it is preferable to use the standard D65 illuminant as an illumination light. It, however, is difficult to obtain an artificial illuminant similar to the standard D65 illuminant. Thus, a relative UV intensity of an illuminant, which is a ratio of the intensity of the illuminant in the UV region against that of the visible region, is calibrated by Gaetner-Griesser method (See xe2x80x9cAssessment of Whiteness and Tint of Fluorescent Substrates with Good Instrument Correlationxe2x80x9d Rolf Griesser, xe2x80x9cThe Calibration of Instruments for the Measurement of Paper Whitenessxe2x80x9d Anthony Bristow/COLOR Research and Application Vol.19 No.6 December 1994).
Details of the calibration of the relative UV intensity of the illuminant is described with reference to FIG. 9. As can be seen from FIG. 9, a fluorescent sample 1 is disposed at a sample aperture 21 for sample of an integration sphere 2. A lamp 101 such as a xenon lamp having a sufficient UV intensity is driven by an emitting circuit 104. A light flux 102 emitted from the lamp 101 enters into the integration sphere 2 through a light source aperture 23. A UV cutoff filter 103 is provided in a manner to cut the light flux 102 partially. A component of UV is removed from the light flux 102 passing through the UV cutoff filter 103. Thus, the relative UV intensity of an illumination light can be calibrated by adjusting the position (insertion ratio) of the UV cutoff filter 103.
The light flux 102 in the integration sphere 2 is diffusely reflected by an inner surface of the integration sphere 2, and diffusely illuminates the fluorescent sample 1. A radiant light 11 radiated from the fluorescent sample 1 passes through an observation aperture 24 and enters into a first spectroscope 105 used for measuring a spectral intensity distribution S(xcex) of the fluorescent sample 1. A reference light 62 having substantially the same spectral intensity distribution of the illumination light enters into an optical fiber 61 by which the reference light 62 is guided to a second spectroscope 106. Thus, the spectral intensity distribution R(xcex) of the reference light 62 is measured by the second spectroscope 106.
For calibrating the relative UV intensity, a non-fluorescent white standard sample 12, in which the reflection spectral radiant factor Brw(xcex) thereof is known, is disposed at the sample aperture 21. A spectral intensity distribution Sw(xcex) of a radiant light from the fluorescent white standard sample 12 and a spectral intensity distribution Rw(xcex) of the reference light are measured. Subsequently, a standard fluorescent sample 13, in which one of perceived color value such as a CIE whiteness thereof is known, is disposed at the sample aperture 21. A spectral intensity distribution S(xcex) of a radiant light from the standard fluorescent sample 13 and a spectral intensity distribution R(xcex) of the reference light are measured. After that, a total spectral radiant factor Bt(xcex) of the standard fluorescent sample 13 is calculated by the above-mentioned equation (3). When the value of the CIE whiteness obtained by using the total spectral radiant factor Bt(xcex) of the standard fluorescent sample 13 is not coincide with the known value of the CIE whiteness of the standard fluorescent sample 13, the position of the UV cutoff filter 103 is adjusted until the calculated a value of the CIE whiteness of the standard fluorescent sample 13 coincides with the known value. In this case, the above-mentioned equation (2) is modified to the following equation (4). Hereupon, the symbol xe2x80x9cpxe2x80x9d designates an attenuation factor in the UV region.
Bf(xcex)=∫UVpxc2x7I(xcexc)xc2x7E(xcexc,xcex)dxcexc/L(xcex)xe2x80x83xe2x80x83(4)
As mentioned above, the Gaetner-Griesser method needs to move the UV cutoff filter 103, so that the configuration of the apparatus is mechanically complex. Furthermore, it is necessary to repeat the movement of the UV cutoff filter 103 and the measurement of the samples 12 and 13 for calibrating the relative UV intensity, so that time will be wasted for the calibration.
For solving the disadvantage of the Gaetner-Griesser method, an apparatus shown in FIG. 10 is proposed (See U.S. Pat. No. 5,636,015). As can be seen from FIG. 10, a first illumination unit 111 and a second illumination unit 121 are provided. A first light flux 113 including a UV component is emitted from a lamp 112 of the first illumination unit 111 and enters into the integration sphere 2 through a first illuminant aperture 22. A light flux including a UV component is emitted from a lamp 122 of the first illumination unit 121 and a UV component is removed therefrom by a UV cutoff filter 123. A second light flux 124 without including the UV component and passing through the UV cutoff filter 123 enters into the integration sphere 2 through a second illuminant aperture 23.
A standard non-fluorescent white sample 12, in which a spectral reflectance W(xcex) is known, is disposed at the sample aperture 21. The lamp 112 of the first illumination unit 111 is lit for measuring a spectral intensity distribution Sw1(xcex) of a radiant light 11 from the standard non-fluorescent white sample 12 and a spectral intensity distribution Rw1(xcex) of a reference light 62. The spectral intensity distributions Sw1(xcex) and Rw1(xcex) are memorized in a memory 108. Subsequently, the lamp 122 of the second illumination unit 121 is lit for measuring a spectral intensity distribution Sw2(xcex) of the radiant light 11 from the standard non-fluorescent white sample 12 and a spectral intensity distribution Rw2(xcex) of the reference light 62. The spectral intensity distributions Sw2(xcex) and Rw2(xcex) are memorized in the memory 108.
Similarly, a standard fluorescent sample 13, in which a total spectral radiant factor BtS(xcex) illuminated by a standard D65 illuminant is known, is disposed at the sample aperture 21. The lamp 112 of the first illumination unit 111 is lit for measuring a spectral intensity distribution S1(xcex) of a radiant light 11 from the standard fluorescent sample 13 and a spectral intensity distribution R1(xcex) of a reference light 62. The spectral intensity distributions S1(xcex) and R1(xcex) are memorized in the memory 108. Subsequently, the lamp 122 of the second illumination unit 121 is lit for measuring a spectral intensity distribution S2(xcex) of the radiant light 11 from the standard fluorescent sample 13 and a spectral intensity distribution R2(xcex) of the reference light 62. The spectral intensity distributions S2(xcex) and R2(xcex) are memorized in the memory 108.
When all the spectral intensity distributions Sw1(xcex), Rw1(xcex), Sw2(xcex), Rw2(xcex), S1(xcex), R1(xcex), S2(xcex) and R2(xcex) are measured, a total spectral radiant factor Bt(xcex) of the standard fluorescent sample 13 is calculated by the following equations (5). Hereupon, symbols a1(xcex) and a2(xcex) respectively designate weight factor.
Bt(xcex)=W(xcex)xc2x7{Sxe2x80x2(xcex)/Rxe2x80x2(xcex)}/{Swxe2x80x2(xcex)/Rwxe2x80x2(xcex)}
Sxe2x80x2(xcex)=a1(xcex)xc2x7S1(xcex)+a2(xcex)xc2x7S2(xcex)
Rxe2x80x2(xcex)=a1(xcex)xc2x7R1(xcex)+a2(xcex)xc2x7R2(xcex)
Swxe2x80x2(xcex)=a1(xcex)xc2x7Sw1(xcex)+a2(xcex)xc2x7Sw2(xcex)
Rwxe2x80x2(xcex)=a1(xcex)xc2x7Rw1(xcex)+a2(xcex)xc2x7Rw2(xcex)
a1(xcex)+a2(xcex)=1xe2x80x83xe2x80x83(5)
When the calculated total spectral radiant factor Bt(xcex) of the standard fluorescent sample 13 does not coincide with the known total spectral radiant factor Bt(xcex) thereof, the weight factors a1(xcex) and a2(xcex) are calculated with respect to each wavelength so as to coincide the calculated value with the known value. Consequently, the relative UV intensity is calibrated.
When the weight factors a1(xcex) and a2(xcex) are calculated, a fluorescent sample 1 which is to be measured is disposed at the sample aperture 21, and the spectral intensity distributions S1(xcex), R1(xcex), S2(xcex) and R2(xcex) of the fluorescent sample 1 are measured. After that, the total spectral radiant factor Bt(xcex) of the fluorescent sample 1 is calculated by following the above-mentioned equation (5).
The prior arts illustrated in the FIGS. 9 and 10 are premised to satisfy the following three conditions. First, an object to be measured is a fluorescent sample including a fluorescent whitening agent which is exited by a UV component of an illumination light and radiates a fluorescence having a wavelength in visible region. Second, the fluorescent sample to be measured includes the fluorescent whitening agent the same as or similar to that of the standard fluorescent sample used in the calibration of the relative UV intensity. Third, the relative UV intensity of the illuminant (especially the light flux 113 from the first illumination unit 111 in the case shown in FIG. 10) is not varied from the calibration of the relative UV intensity to the measurement of the sample.
The above-mentioned first and second conditions can be satisfied by restricting the object to be measured. It, however, is not realistic to be satisfied the third condition because of the following reasons. There is a phenomenon called xe2x80x9cintegration sphere effectxe2x80x9d that reflected light from the sample and fluorescence from the sample (intensity distribution of the fluorescent whitening agent generally has a peak in the vicinity of the wavelength 450 nm) are included in the illumination light in the integration sphere 2. Furthermore, the UV intensity of the light source will be reduced due to the deterioration of the illuminant with age.
When the relative UV intensity of the light source is varied between the calibration and the measurement of the sample, the fluorescent spectral radiant factor Bf(xcex) includes error component, as can be seen from the above-mentioned equation (2). Such the error component causes the error of the total spectral radiant factor Bt(xcex) obtained from the fluorescent spectral radiant factor Bf(xcex).
The error component caused by the deterioration of the light source can be reduced by shortening a time period of a cycle of the calibration of the relative UV intensity. It, however, is difficult to reduce the error component caused by the integration sphere effect, since this phenomenon depends on the characteristics of the sample.
An object of this invention is to provide an apparatus and a method for measuring a spectral property of a fluorescent sample including a fluorescent material, in which the variation of the relative UV intensity of the light source due to the deterioration of the light source and the integration sphere effect can be calibrated, and the error component in the measurement result due to the variation of the relative UV intensity can be reduced.
An apparatus for measuring a spectral property of a fluorescent sample including a fluorescent material in accordance with this invention comprises a first and second illumination units, a first and second spectroscopes, a memory, a measurement controller and a first to a third processors.
The first illumination unit emits a first illumination light including a ultraviolet component, and the second illumination unit emits a second illumination light including a component having a wavelength longer than a predetermined cutoff wavelength.
The first spectroscope measures a spectral intensity distribution of a radiant light radiated from a sample disposed at a measurement position when the sample is illuminated by the first or second illumination unit, and the second spectroscope measures a spectral intensity distribution of a reference light which is similar to the illumination light from the first or second illumination unit when the sample is illuminated by the illumination light.
The memory memorizes a weight factor.
The measurement controller alternatively controls the first and second illumination units for illuminating a fluorescent sample to be measured at the measurement position, controls the first spectroscope for measuring alternative of a first measured radiant light spectral intensity distribution of a radiant light radiated from the fluorescent sample corresponding to the illumination light from the first illumination unit and a second measured radiant light spectral intensity distribution of a radiant light radiated from the fluorescent sample corresponding to the illumination light from the second illumination unit, and controls the second spectroscope for measuring alternative of a first measured reference light spectral intensity distribution of a reference light corresponding to the illumination light from the first illumination unit and a second measured reference light spectral intensity distribution of a reference light corresponding to the illumination light from the second illumination unit.
The first processor calculates a first total spectral radiant factor of the fluorescent sample by using the first measured radiant light spectral intensity distribution and the first measured reference light spectral intensity distribution, and a second total spectral radiant factor of the fluorescent sample by using the second measured radiant light spectral intensity distribution and the second measured reference light spectral intensity distribution.
The second processor calculates a first corrected total spectral radiant factor by using a ratio of an intensity in a visible portion of the first standard reference light spectral intensity distribution against an intensity in a ultraviolet portion thereof, and a ratio of an intensity in a visible portion of the first measured reference light spectral intensity distribution against an intensity in a ultraviolet portion thereof.
The third processor calculates a total spectral radiant factor of the fluorescent sample by using the corrected total spectral radiant factor, the second total spectral radiant factor and the weight factor.
By such a configuration, the fluorescent sample to be measured disposed at the measurement position is illuminated by the illumination light from the first illumination unit including the UV component, and the first radiant light spectral intensity distribution and the first reference light spectral intensity distribution are measured by the first and second spectroscopes. Furthermore, the first total spectral radiant factor of the fluorescent sample is calculated from these spectral intensity distributions by the first processor.
Subsequently, the fluorescent sample is illuminated by the second illumination light from the second illumination unit without including the UV component, and the second radiant light spectral intensity distribution and the second reference light spectral intensity distribution are measured by the first and second spectroscopes. Furthermore, the second total spectral radiant factor of the fluorescent sample is calculated from these spectral intensity distributions by the first processor.
The first total spectral radiant factor of the fluorescent sample is corrected to the corrected total spectral radiant factor by the second processor in a manner so that the corrected total spectral radiant factor is similar to the total spectral radiant factor of the fluorescent sample when the fluorescent sample is illuminated by the same illumination light at the setting of the weight factor.
The third processor calculates the total spectral radiant factor of the fluorescent sample as a measurement result by linear combination of the weighted corrected total spectral radiant factor and a weighted second total spectral radiant factor by using the weight factor. As a result, an error component due to the variation of the illumination lights in a time period from the first and second illumination units from the setting of the weight factor to the measurement of the fluorescent sample can be reduced, and the accuracy of the measurement result can be increased.